Enable tests on OS X too.

Add Travis badge.

.travis.yml

@@ -1,7 +1,10 @@
 language: c
 script: ./.travis.sh
+os:
+    - linux
+    - osx
 env:
-- TARGET=host
-- TARGET=arm32
+    - TARGET=host
+    - TARGET=arm32
 notifications:
-  email: false
+    email: false

README.md

@@ -1,5 +1,7 @@
 ## OpenLibm
 
+[![Build Status](https://travis-ci.org/JuliaLang/openlibm.svg?branch=master)](https://travis-ci.org/JuliaLang/openlibm)
+
 [OpenLibm](http://www.openlibm.org) is an effort to have a high quality, portable, standalone
 C mathematical library ([`libm`](http://en.wikipedia.org/wiki/libm)).
 It can be used standalone in applications and programming language